The 3C33 is a twin triode power amplifier. The circuit given in the datasheet shows the valve being used as a switch driven hard by a square wave generator.
The RCA Transmitting Tube manual describes the 3C33 as being for industrial control and voltage regulation.
Thanks to Bob Hopkins for sending the image.
The wide glass tube envelope is 48 mm in diameter, and excluding the B8A base pins is 78 mm tall.
Reference: Datasheet & 4038. Type 3C33 was first introduced in 1946.
Absolute Maximum Operating Conditions¶
Updated February 20, 2013. shape:wide.glass.tube construction:all.glass type:double.triode age:1940.1950 base:b7a heater:12.6v pins:7 pin:1.h pin:2.g1(2) pin:3.a(2) pin:4.k pin:5.a(1) pin:6.g1(1)